Glass composition for electrical discharge devices



Patented Aug. 7, 1934 7 operation of the device the cadmium vapor "'11,969, 27f7 11 GLAss ooMros 'rlonroa ELECTRICAL" msonimosnrzvlonsMarcello Pirani, Berlin;Wilmersdorfgillrlartin Roger, Berlin, Pankow,Germany,

and Georg,

assignors to General Elec- Gaidies, Berlintric Company, a corporation 02New York No Drawing.

Serial No. 1930 The present invention relates to gaseous electricdischarge devices generally and more particularly the invention relatesto such devices in which the gaseous content is a metal vapor, or inwhich a metal vapor is a component of the gaseous content.

It is well known in the art that a gaseous electric discharge devicehaving a filling of cadmium metal vapor emits a pleasing greenish bluelight; however, it is also well known in the art that such cadmium vaporfilled electric discharge devices have hitherto been of slight practicaluse because the cadmium vapor con- 7 denses readily at temperaturesabove the melting temperatures of the usual glasses used in thecontainers of such devices, and further the glass container of suchdevices becomes coatedwith a brown or black coating after a short periodof to change the color of discharge.

It is the object of this invention to produce a glass suitable for usein the arts generally and particularly as the container for cadmiumvapor filled electric discharge devices. We have discovered that such aglass having the desired.

characteristics of being easily workable, highly heat resisting, andchemically stable in the presence of an alkali metal vapor such as acadmium vapor filling for example, may be produced if a boro-silicateglass containing besides the usual boric acid, alkalies, and alkaliearths also contains at least 10% aluminum oxide (A1203) and less than60% silicic acid (S102), where the proportions are given in percentagesby weight.

w A glass container made in accordance with the above formula does notbecome noticeably browned or blackened after 1,000 hours of operation aswe have proven by experiment. I

A suitable glass is produced if the constituents are mixed inpercentages by weight according to the following formula:--

40 to 60% boric oxide (B203) 4 to 5% sodium oxide (NazO) to 11% calciumoxide (CaO) 11 to 13% alumina (A1203) to silica (S102) A particularlygood glass of the above type for the containers of electric dischargedevices having alkali metal vapor fillings is a glass hav- ApplicationJanuary 510,222. In Germany February 8,

,5 Claims. (014065361) T 1 ing the following composition in percentagesby weight:-

% boric oxide B203) 4% sodium oxide (Na'zO) 11% calcium oxide-(CaO) 13%alumina (A1203) 7 22% silica (SiOz) It is possible to reduce the alkaliand alkali earth content of the boric acid part of the glass slightlyand to replace these by additional amounts of aluminum oxide and silicicacid in accordance with the following formula:-

8.5 to 15% boric oxide (B203) 1.2 to 2% sodium oxide and (Na2O+K2O) 13to 15% calcium oxide and magnesium oxide (Ca0+MsO) 19 to 23% alumina(A1203) 40 to silica (SiOz) A particularly good glass of the above typefor the containers of electric discharge devices having alkali metalvapor fillings is a glass potassium oxide having the followingcomposition in percentages by weight- 15% boric oxide (B203) 2% sodiumoxide and potassium oxide (N&20+K20) 15% calcium oxide and magnesiumoxide (Ca0+MgO) 23% alumina (A1203) 45% silica (S102) The silicic acidof the bore-silicate glass in both cases may be replaced in part, forexample, up to one half, by the oxides of rare earths,

such as the oxides of lanthanum or didymium,

or by a mixture of such oxides.

As the glass disclosed above is slightly hygroscopic it is desirablethat the container of an electric discharge device made of such glass beprotected from the surrounding atmosphere by a covering or casing madeof a non-hygroscopic glass well known in the art, such as Thiiringerglass, which has a better acid, lye and water stability than theboro-silicate glass of the present invention. 'Thiiringer glass and thebore-silicate glass of this invention have approximately the samecoefficients of expansion and are capable of being fused together toform a double walled or a single walled two-layer container where thatis desired. Where desired the Thiiringer glass may be replaced by a heatabsorbing glass, such as the Schottshen glasses BG 9 and BG 10, whichabsorb the heat radiating from the electric discharge and which areraised to a high temperature to prevent condensation of the metal vapor,such as cadmium vapor, and a consequent loss of vapor pressure even withan extremely cold outside temperature.

Where desired the non-hygroscopic glass has a widely difierentcoefiicient of expansion than the boro-silicate glass of the presentinvention provided there is no point of fusion between the outercontainer" made of the non-hygroscopic glass and the inner containermade of the bore-silicate glass of the present invention and the currentleads sealed into each container' have difierent coefi-icients ofexpansion over their length to correspond approximately to that of theglass containers at the of said Wires in said containers.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. A glass containing between 40 to 60% boric oxide (B203) 4 to 5%sodium oxide (Na2O) 10 to 11% calcium oxide (CaO) 11 to 13% alumina(A1203) 20 to 30% silica (Si02).

sealing in points 2. A glass containing1- 50% boric oxide (B203) 4%sodium oxide (Na2O) 11% calcium oxide (CaO) 13% alumina (A1203) 22%silica (Si02).

3. A glass containing the usual glass bases 2 as alkalies, alkaliearths, and boric oxide mixed with not less than 10% aluminum oxide(A1203) and not less thanabout 20% and less than 60% silica (Si02). 1

4. A glass containing between 8.5 to 15% boric oxide (B203) 1. 2 to 2%sodium oxide and potassium oxide (Na2O+K2O) 13 to 15% calcium oxide andmagnesium oxide (CaO-l-MgO) 19' to 23% alumina (A1203) 40 to 60% silica(S102), 5. A glass containing 15% boric oxide (B203) 2% sodium oxide,and potassium oxide (Na2O+K2O) V I 15% calcium oxide and magnesium oxide(Ca0+MgO) 23% alumina (A1203) 45+silica (SiO2). V

' MARCELLO PIRANI.

MARTIN REGER. GEORG GAIDIES.

